I believe both TVs use the same LCD panel, but Sony uses a different backlighting system which yields slightly better results; both are excellent, though. Personally, I would stay away from the Sharps, as this past generation has had many reports of large swaths of banding in the displays linked to a manufacturing problem; supposedly the problem has been resolved, but the prices of this coming generation have supposedly gone up. But let's get back to the facts...
Both are superb. The extra cost of the Sony goes to the casing, the backlighting system, more picture tweaking ability without getting into service-level menus, superior standard-def performance, and the name Sony. Is all of this worth the difference in price? That's up to you.
If you're looking for someone to say which one performs better, on an absolute scale, the Sony performs better. Which one is a better vaule? Because the performance difference is slight, I'd say the Samsung is a better deal. But I can't tell you which one is better for you. (Right Bill?)
They're both great TVs. No need to second-guess yourself... Go with your gut.